Vapor generator



J1me 1964 A. M. FRENDBERG ETAL 3,136,298

VAPOR GENERATOR Filed June 2'7, 1962 3 Sheets-Sheet 1 FIG. 1

INVENTORS Thomas B. Hursr BY Ari-hur M. Frendberg ATTORNEY June 1964 A. M. FRENDBERG ETAL 3,136,298

VAPOR GENERATOR Filed June 27, 1962 3 Sheets-Sheet 2 FIG.2

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INVENTORS Thomas B. Hursr BY Arfhur M. Frendberg ATTORNEY VAPOR GENERATOR Filed June 2'7, 1962 5 Sheets-Sheet 3 INVENTORS Thomas B. Hursr BY Arrhur M Frendberg ATTORNEY United States Patent 3,136,298 VAFOR GENERATOR Arthur M. Frendherg and Thomas B. Hurst, Akron, Ohio, assignors to The Bahcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed June 27, 1962, Ser. No. 205,662 5 Claims. (Cl. 12233d) This invention relates to an improved vapor generator and heating apparatus and more particularly to a compact, integral, bottom-supported, gas and/ or oil fired, pressurized furnace steam generator desi ned for power, process, or heating loads requiring steam capacities in the range of 450,000 to 900,000 pounds per hour and with steam temperatures ranging as high as 900 F. and design pressures in the range of 250 to 1200 p.s.i.

The invention herein disclosed is an improvement over the integral furnace vapor generator disclosed in US. Patent No. 3,003,482, whereby the capacity of a unit employing the same desirable basic design features of such a unit can be adapted to substantially increased and even double the maximum steam output of the unit of US. Patent 3,003,482. Capacities above 450,000 pounds of steam per hour have heretofore not been possible with a unit of this type because of limitations imposed by the upper or steam drum, steam-water separating capacity, gas-pass sizing, and burner spacing with respect to adjacent furnace walls.

With bottom-supported units of this type, it is not desirable to increase the overall vertical height of the boiler bank and/or the diameter of the steam drum established with respect to US. Patent 3,003,482 because of drum support problems. If the distance between drum centers were materially increased, larger diameter generating tubes would have to be used, or internal or external support members would have to be added to support the increased weight of the upper drum. For this reason, and for the purpose of maintaining low profiles for seismic and windload structural requirements, it is advantageous to maintain the vertical height of the boiler bank or the distance between drum centers at the minimum commensurate with satisfactory circulation design. This dictates that increased capacity should preferably be obtained by increasing furnace width. In the patented vapor generator cited, the length of the steam drum cannot be indiscriminately increased to provide additional drum capacity because of fluid flow considerations within the steam drum. A further increase in steam capacity accompanied by an increase in drum length could cause an excessive drum level gradient and water level control difficulties with attendant steam-water separation and carry-over problems.

As the gas fiow through the patented unit is increased, as dictated by an increase in steam output, the draft loss would increase as a square function of gas mass flow unless the gas pass sizes are proportionately increased. On

the other hand, appropriate increases in the gas pass sizes to maintain reasonable draft losses therethrough would result in such large gas passes that maldistribution of gases within the passes would occur.

It is an object of the present invention to provide a bottom-supported steam generating and heating apparatus, employing the desirable features of the unit disclosed in US. Patent No. 3,003,482, having a steam output capacity in the range of 450,000 to 900,000 pounds per hour, and requiring a minimum of space in relation to its steam output capacity. It is a further object of this invention to provide this capacity increase without increasing the height of the generating unit, and without increasing the steam drum diameter. It is a further object of this invention to optimize conditions in the steam drum with respect to flow conditions within the steam drum, and to provide a aliases Patented June 9, 1964 gas flow pattern that results in elficient heat transfer with reasonable draft loss.

In accordance with the invention, the vapor generating unit comprises water walls including fluid heating tubes which form a setting which is suitably divided by a partition wall into the furnace and a boiler tube bank, the latter being arranged within two symmetrical parallel heating gas passes the one of which is of opposite hand to the other. The gas passes have separate gas inlets communieating with the furnace adjacent the furnace sidewalls, and are defined in part by the dividing partition wall. A gas outlet, common to booth heating gas passes, is at the center rear of the setting. A bank of steam generating tubes, provided in each of the heating gas passes, extends between a vertically aligned upper horizontal steam and water drum and a lower horizontal water drum which extends transversely of the settting. A bank of downcomer tubes is disposed in the common gas outlet of the heating gas passes and extends between and is connected to the center portions of the upper and lower drums. A suitable number of rows of screen tubes are connected between the drums and are disposed in and extendacross the full width of the furnace at a position near the partition wall. A bank of superheater tubes is spaced across the Width of the furnace symmetrical with respect to the setting sidewalls, and originating in the top of the steam and water drum in a substantially symmetrical pattern with respect to the longitudinal center of the upper drum. The superheater tubes are spaced in relation to the screen tubes so as to combine radiation and convection heat transfer characteristics relative to the hot combustion gases in the furnace. Hot combustion gases, supplied to the furnace by burning fuel, pass longitudinally through the furnace, over the secreen tubes and superheater tubes, and then divide into parallel, symmetrical heating gas passes. The latter portions of the heating gas passes, in a gas flow sense, permit the gas streams to combine and form a common gas outlet at the rear center of the setting.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a sectional side view of the steam gener-' ator taken along line 1-1 of FIGURE 2;

FIGURE 2 is a sectional plan view taken along line 2--2 of FIGURE 1; and

FIGURE 3 is a sectional plan view taken along line 3-3 of FIGURE 1.

In the drawings the invention has been illustrated as a bottom-supported, natural circulation, integral steam generating unit designed primarily for oil and/ or gas firing for operation at super-atmospheric pressure in the furnace and available in sizes for outputs ranging between 450,000 and 900,000 pounds of steam per hour at pressures and temperatures respectively as high as 900 F. and 1200 psi. The furnace and boiler heating surface necessary to obtain a certain steam output is usually attained by varying the side-Wall to side-wall dimension while holding the cross-section as seen in the side view substantially constant. By prefabricating portions of the unit in the factory, a better quality finished product is assured, and a minimum of labor and erection time are required to erect the unit and ready it for commercial service. The bottom support feature is conducive to comparatively simple foundation structure, eliminating the necessity for costly external steelwork with consequent saving both in the time and cost of field erection.

Referring to FIGURES 1 and 2, the steam generating unit comprises a furnace-boiler settting of substantially rectangular cross-section in both elevation and plan sections having upright front and rear walls 1% and 11, respectively upright opposing side walls 12 and 13, a slightly upwardly sloping enclosing wall or roof 14, and a slightly downwardly sloping enclosing wall or floor 15 defining a furnace cavity 16 and a heating gas pass section 17. The furnace cavity 16 and heating gas pass 17 are separated by laterally extending partition or baffle wall 20 which extends vertically from the floor 15 to the roof 14 and at the lateral extremities of which are the inlet openings 21A and 22A to the parallel, opposite hand, and symmetrical heating gas passes 21 and 22. The heating gas passes 21 and 22 are further subdivided by parti tions 23 and 24 which extend forwardly into the gas pass perpendicular to the rear wall 11 to form a final heating gas pass 25 common to the heating gas passes 21 and 22. The gas outlet 26 in the rear wall 11 provides the exit for gases from the final gas pass 25.

By providing parallel heating gas passes 21 and 22 the draft loss through the heating gas pass section can be maintained at a resonable level even at high steam outputs, while the individual passes are maintained of such size as not to be conducive to maldistribution of gas within the passes. The arrangement involving a common last pass 25 leading to the gas outlet 26 is equally advantageous since it eliminates the expense of separate outlet ducting which would normally be required on a unit having a split or divided gas flow pattern. By making the gas passes parallel, symmetrical, and of opposite hand, uniform distribution of heating gases between the passes is assured. The partitions or baffles 23 and24 require the gas flowing through the generating unit to make an additional turn, and thus optimize the cross-flow heat transfer conditions in the heating gas passes.

The heating gas passes 21 and 22 have banks of upwardly extending tubes 30 of relatively small diameter disposed across the width of the passes. The upper ends of the tubes open into a horizontally disposed upper steam and water drum 31 and their lower ends into a horizontally arranged lower water drum 32. The upper and lower drums 31 and 32 respectively have their horizontal axes in a common vertical plane parallel to the front and rear walls and 11 of the setting.

The cross flow of gases over the tubes 30 provides the most advantageous use of this convection heat absorbing surface and contributes to the high steam generating capacity in relation to the space occupied by the tube banks. The end portions of the tubes 30 extend radially from the drums 31 and 32 with the intermediate tube portions b ing vertical.

A bank of downcomer tubes 37 is provided in the area of lowest gas temperature within the settting; namely, in the centrally located common gas pass 25. The downcomer tubes 37 are connected to and open into the longitudinal center portions of the drums 31 and 32 with radially extending ends and vertical central tube positions similar in contour to the aforementioned generating tubes 39. By symmetrical positioning of the downcomer tubes so that water flow to the downcomer bank from within the steam and water drum 31 is toward its central portion, the maximum permissible drum capacity per unit of drum length for a given drum diameter without encountering unstable water level and attendant steamwater separation problems is effectively twice that which could be used if the downcomer tubes were located at one end of the drum. Thus, by positioning the final heating gas pass 25 between the central portions of the drums 31 and 32, and the downcomer tubes 37 therein, flow conditions in the upper steam and water drum 31 will be optimized and the resulting water level gradient will be minimized so that maximum steam output may be obtained while retaining a practicable drum size.

As shown in FIGURES l, 2, and 3, the tubes forming the side walls 12 and 13 are supplied with water from the lower drum 32 through supply tubes 33 to the lower side wall headers 34 to which the side wall tubes are connected. The upper portions of the tubes in the side walls 12 and 13 open into the upper side wall headers 35, and the steam and water mixture discharge from the side wall tubes is conveyed to the upper steam and water drum 31 by discharge tubes 36. It is to be noted that the furnace sidewalls 12 and 13 and their respective supply and riser tubes are similar in every respect, except that one is the opposite hand of the other. Hence, common reference numbers have been employed for convenience.

The partition wall 29 specifically includes the centrally disposed tubes of the forwardmost row of upwardly ex tending tubes 35 in the steam generating bank. it 13 formed by spaced tubes of relatively small diameter which have their intertube spaces closed by refractory covered retallic members welded to the tubes along their length so that the wall is substantially imperforate to gas flow. The partition walls 23 and 24 are formed of metallic plates suitably positioned between two adjacent tube rows defining the sides of the last gas pass 25 as shown in MG- URE'Z.

Rows of screen tubes 4t extending laterally between the side walls 12 and 13 are provided parallel to and slightly forward of the partition wall 20. The number and configuration of the rows of screen tubes 44) Will depend for the most part on the desired superheater performance which is hereinafter described. Each screen tube 43 opens into and extends radially outwardly from the steam drum 31, then generally forward and substantially parallel to the roof 14, then downwardly parallel to the partition wall 20, then rearwardly substantially parallel to the floor 15, and then radially into the lower drum 32.

In FIGURE 1, a drainable superheater 42 is shown including several rows of superheater tubes 41 disposed within the cavity defined by the tube row comprising the partition wall 20 and the innermost row 40A of screen tubes 40. In the embodiment shown, superheater tube extension 43 of tubes 41 are connected to the top of the steam and water drum 31 along its entire length and are bent forwardly, then downwardly and pass through the roof 14 into the setting and become the superheater tubes 41. The tubes 4-1 extend vertically downward through the setting, through the floor 15 and open into a superheated steam collecting header which underlies the floor 15 transversely of the setting forward of and parallel to the lower drum 32. As shown in FIGURE 3, a superheater outlet header 45 is connected perpendicular to and extends rearwardly from the center of the collecting header 44.

The superheater tubes 41 are positioned in the cavity between the partition wall 20 and the innermost row of screen tubes 46A so as to be aligned between the screen tubes 40 so that the superheater tubes 41 see the radiant gases in the furnace cavity 16. The superheater 42 will be absorbing heat by both radiation and convection so that the variation in superheater outlet temperature normally experienced in conjunction with varying unit loads will be minimized, particularly when convection is the principal heat transfer mechanism.

The superheater 42 shown in this particular embodiment of the invention is designed for relatively low superheater outlet temperature, i.e., 600 F.; however, it should be recognized that more or less superheat can be obtained by varying the amount and location of the superheater tubes 41 in relation to the screen tubes 49. For example, a two-pass superheater could be employed by providing an additional superheated steam collecting header under the setting with appropriately positioned inverted, drainable, U-shaped superheater tubes connecting the collecting headers. Obviously, the quantity of vapor generating surface in the heating gas passes can also be adjusted replacing steam generating surface with superheater surface as final steam temperature requirements might dictate.

Combustion gases are supplied to the furnace cavity 16 by burning gaseous and/ or liquid fuel using the fuel burners 50 which are mounted in the front wall 10. Fuel is supplied to the burners 50 through appropriate piping, and air is supplied through a plenum windbox 51 which surrounds substantially all of the roof 14 and the front wall of the setting. The furnace roof 14 and front wall 10 are encased by an airtight plenum-windbox 51 for conducting combustion air to the burners 50. With this arrangement, heat which would normally be lost through an exterior casing is advantageously utilized to heat the combustion air. Air enters the windbox 51 through and air inlet 55 provided in the rear windbox boundary wall 54, passes over the roof 14 of the setting, and downwardly to the burners 50 mounted in the front wall 10.

While in accordance with the provisions of the statutes there is illustrated and described herein a specific embodiment of the invention, those skilled in the art will understand that changes may be made in the form of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of the other features.

What is claimed is:

1. A steam generator comprising a front wall, a rear wall, and a pair of oppositely disposed side walls arranged to form a substantially rectangular setting, an upright partition wall extending transversely of said setting and dividing said setting into a furnace and a vapor generating section extending across the entire width of said setting, means dividing said section into a pair of parallel flow gas passes arranged on opposite sides of said section and a common gas pass disposed intermediate and opening to said parallel gas passes, the opposite lateral ends of said partition wall being spaced from their respective adjacent side walls to form therebetween a pair of heating gas inlets leading from said furnace to said pair of parallel gas passes, an upper horizontal steam and water drum extending across the entire width of said setting and overlying said vapor generating section and having opposite end portions and a central portion intermediate said end portions, a lower horizontal water drum extending transversely of said setting and underlying said vapor generating section, a bank of steam generating tubes disposed in each of said parallel gas passes and at least a major portion of which extend between and connect into said upper and lower drums along the end portions thereof, and a bank of downcomer tubes disposed in said common gas pass and extending between and connected substantially only into the longitudinally central portions of said upper and lower drums, said upper drum cooperating with said steam generating tubes and said downcomer tubes to effect the flow of water from the end portions to the central portion of said upper drum to minimize water level gradient therein.

2. A steam generator comprising a front wall, a rear wall, and a pair of oppositely disposed side walls arranged to form a substantially rectangular setting, an upright partition wall extending normal to said side walls and dividing said setting into a furnace and a vapor generating section extending across the entire width of said setting, means dividing said section into a pair of parallel flow gas passes arranged on opposite sides of said section and a common gas pass disposed intermediate and opening to said parallel gas passes, the opposite lateral ends of said partition wall being spaced from their respective adjacent side walls to form therebetween a pair of heating gas inlets leading from said furnace to said pair of parallel gas passes and being in the same plane as said partition wall, an upper horizontal steam and water drum extending across the entire width of said setting and overlying said vapor generating section and having opposite end portions and a central portion intermediate said end portions, a lower horizontal water drum extending transversely of said setting and underlying said vapor generating section, a bank of steam generating tubes disposed in each of said parallel gas passes and at least a major portion of which extend between and connect into said upper and lower drums along the end portions thereof, and a bank of downcomer tubes disposed in said common gas pass and extending between and connected substantially only into the longitudinally central portions of said upper and lower drums, said upper drum cooperating with said steam generating tubes and said downcomer tubes to effect the flow of water from the end portions to the central portion of said upper drum to minimize water level gradient therein.

3. A steam generator comprising a front wall, a rear wall, and a pair of oppositely disposed side walls arranged to form a substantially rectangular setting, an upright partition wall extending transversely of said setting and dividing said setting into a furnace and a Vapor generating section extending across the entire width of said setting, means dividing said section into a pair of parallel flow gas passes symmetrically arranged on opposite sides of said section and a common gas pass disposed intermediate and opening to said parallel gas passes, one of said parallel flow gas passes being formed as a mirror image of the, other of said parallel flow gas passes, the opposite lateral ends of said partition wall being spaced from their respective adjacent side walls to form therebetween a pair of heating gas inlets leading from said furnace to said pair of parallel gas passes, an upper horizontal steam and water drum extending across the entire width of said setting and overlying said vapor generating section and having opposite end portions and a central portion intermediate said end portions, a lower horizontal water drum extending transversely of said setting and underlying said vapor generating section, an equal bank of steam generating tubes disposed in each of said parallel gas passes and at least a major portion of which extend between and connect into said upper and lower drums along the end portions thereof, and a bank of downcomer tubes disposed in said common gas pass and extending between and connected substantially only into the longitudinally central portions of said upper and lower drums, said upper drum cooperating with said steam generating tubes and said downcomer tubes to effect the flow of water from the end portions to the central portion of said upper drum to minimize water level gradient therein.

4. A steam generator comprising a front wall, a rear wall, and a pair of oppositely disposed side walls arranged to form a substantially rectangular setting, an upright major partition wall extending transversely of said setting and dividing said setting into a furnace and a vapor generating section extending across the entire width of said setting, means forming a heating gas outlet in the lateral central portion of said vapor generating section, a pair of minor partition walls extending normal to said rear wall into said vapor generating section, said major and minor partition walls cooperating to divide said section into a pair of parallel fiow gas passes arranged on opposite sides of said section and a common gas pass disposed intermediate and opening to said parallel gas passes and said heating gas outlet, the opposite lateral ends of said major partition wall being spaced from their respective adjacent side walls to form therebetween a pair of heating gas inlets leading from said furnace to said pair of parallel gas passes, an upper horizontal steam and water drum extending across the entire width of said setting and overlying said vapor generating section and having opposite end portions and a central portion intermediate said end portions, a lower horizontal water drum extending transversely of said setting and underlying said vapor generating section, a bank of steam generating tubes disposed in each of said parallel gas passes and at least a major portion of which extend between and connect into said upper and lower drums along the end por- 7 tions thereof, and a bank of downcomer tubes disposed in said common gas pass and extending between and connected substantially only into the longitudinally central portions of said upper and lower drums, said upper drum cooperating with said steam generating tubes and said 5 downcomer tubes to effect the flow of water'frorn the end portions to the central portion of said upper drum to minimize Water level gradient therein.

5. A steam generator comprising a front wall, a rear wall, and a pair of oppositely disposed side walls arranged to form a substantially rectangular setting, a vertically disposed major partition wall extending normal to said side walls and dividing said setting into a furnace and a vapor generating section extending across the entire width of said setting, means forming a heating gas outlet in the lateral central portion of said vapor generating section, a pair of minor partition walls extending normal to said rear wall into said vapor generating section, said major and minor partition Walls cooperating to divide said section into a pair of parallel flow gas passes symmetrically arranged on opposite sides of said section and a common gas pass disposed intermediate and opening to parallel gas passes and said heating gas outlet, one of said parallel flow gas passes being formed as a mirror image of the other of said parallel flow gas passes, the opposite lateral ends of said major partition wall being spaced from their respective adjacent side walls to form therebetween a pair of heating gas inlets leading from said furnace to said pair of parallel gas passes and being in the same plane as said major partition wall, an upper horizontal steam and water drum extending, across the entire width of said setting and overlying said vapor generating section and having opposite end portions and a central portion intermediate said end portions, a lower horizontal water drum extending transversely of said setting and underlying said vapor generating section, an equal bank of steam generating tubes disposed in each of said parallel gas passes and at least a major portion of which extend between and connect into said upper and lower drums along the end portions thereof, and a bank of downcomer tubes disposed in said common gas pass and extending between and connected substantially only into the longitudinally central portions of said upper and lower drums, said upper drum cooperating with said steam generating tubes and said downcomertubes to effect the flow of water from the end portions to the central portion of said upper drum to minimize water level gradient therein.

,References Cited in the file of this patent UNITED STATES PATENTS 3,003,482 Hamilton 'et al. Oct. 10, 1961 3,022,774 Hamilton et a1, Feb. 27, 1962 FOREIGN PATENTS 80,520 Netherlands Feb. 15, 1956 

1. A STEAM GENERATOR COMPRISING A FRONT WALL, A REAR WALL, AND A PAIR OF OPPOSITELY DISPOSED SIDE WALLS ARRANGED TO FORM A SUBSTANTIALLY RECTANGULAR SETTING, AN UPRIGHT PARTITION WALL EXTENDING TRANSVERSELY OF SAID SETTING AND DIVIDING SAID SETTING INTO A FURNACE AND A VAPOR GENERATING SECTION EXTENDING ACROSS THE ENTIRE WIDTH OF SAID SETTING, MEANS DIVIDING SAID SECTION INTO A PAIR OF PARALLEL FLOW GAS PASSES ARRANGED ON OPPOSITE SIDES OF SAID SECTION AND A COMMON GAS PASS DISPOSED INTERMEDIATE AND OPENING TO SAID PARALLEL GAS PASSES, THE OPPOSITE LATERAL ENDS OF SAID PARTITION WALL BEING SPACED FROM THEIR RESPECTIVE ADJACENT SIDE WALLS TO FORM THEREBETWEEN A PAIR OF HEATING GAS INLETS LEADING FROM SAID FURNACE TO SAID PAIR OF PARALLEL GAS PASSES, AN UPPER HORIZONTAL STEAM AND WATER DRUM EXTENDING ACROSS THE ENTIRE WIDTH OF SAID SETTING AND OVERLYING SAID VAPOR GENERATING SECTION AND HAVING OPPOSITE END PORTIONS AND A CENTRAL PORTION INTERMEDIATE SAID END PORTIONS, A LOWER HORIZONTAL WATER DRUM EXTENDING TRANSVERSELY OF SAID SETTING AND UNDERLYING SAID VAPOR GENERATING SECTION, A BANK OF STEAM GENERATING TUBES DISPOSED IN EACH OF SAID PARALLEL GAS PASSES AND AT LEAST A MAJOR PORTION OF WHICH EXTEND BETWEEN AND CONNECT INTO SAID UPPER AND LOWER DRUMS ALONG THE END PORTIONS THEREOF, AND A BANK OF DOWNCOMER TUBES DISPOSED IN SAID COMMON GAS PASS AND EXTENDING BETWEEN AND CONNECTED SUBSTANTIALLY ONLY INTO THE LONGITUDINALLY CENTRAL PORTIONS OF SAID UPPER AND LOWER DRUMS, SAID UPPER DRUM COOPERATING WITH SAID STEAM GENERATING TUBES AND SAID DOWNCOMER TUBES TO EFFECT THE FLOW OF WATER FROM THE END PORTIONS TO THE CENTRAL PORTION OF SAID UPPER DRUM TO MINIMIZE WATER LEVEL GRADIENT THEREIN. 